The present invention relates to aircraft propulsion systems, and more particularly to control systems for mitigating contrail formation.
Contrails, also known as condensation trails or vapour trails, are line-shaped ice-clouds that appear behind aircraft under certain circumstances. The formation of a contrail depends on a number of factors, including: ambient temperature, humidity and pressure; the efficiency of the aircraft's engines; and the properties of the fuel burned in the engines.
A contrail, once formed, will typically dissipate within a minute or so, unless the ambient air is supersaturated with respect to ice, in which case the contrail may persist. A persistent contrail will grow over time to resemble natural cirrus cloud, both in size and optical properties, and is referred to as “contrail-cirrus”. Line-shaped contrails and contrail-cirrus are collectively referred to as “aviation-induced cloudiness” (AIC). Contrail-cirrus is thought to cause a majority of the climate impact of AIC due to it being spatially-larger and longer-lived than non-persistent line-shaped contrails.
Depending on the metric employed, the climate-warming impact of aviation-induced cloudiness may be of a similar magnitude to that of the CO2 emitted by aircraft, and may therefore represent a significant element of aviation's total climate impact. The control of contrail formation and/or contrail properties, and particularly the reduction of the impact of persistent contrails, therefore represents a compelling opportunity for a significant reduction in the overall climate warming impact of aviation.
However a number of potential techniques for suppression of contrail formation by a gas turbine engine require the use of bespoke equipment and/or materials that are additional to those required for conventional engine operation. Any weight and/or energy penalties incurred in order to achieve contrail suppression require careful scrutiny to determine whether such penalties outweigh the possible contrail reduction benefits on climate impact.
Another method of potentially reducing the negative impact of contrail formation is to route aircraft around/above/below regions of air susceptible to contrail formation and/or persistence. However, in addition to the added complexity for air traffic control and pilots, the re-routing of aircraft away from predetermined flight paths will cause increased fuel burn, not only by increasing duration and distance travelled, but also by causing departure from optimal cruise conditions of the aircraft engines.
It is therefore an object of the present invention to manage the formation and/or characteristics of aircraft engine exhaust contrails in a manner that reduces negative impact on the climate. It may be considered an additional or alternative aim to provide a system for aircraft engine contrail mitigation which bears minimal weight penalty.